<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">

    <title>Document</title>
    <style>
        .a {
            width: 5rem;
            height: 5rem;
            background-color: #f00;
        }
    </style>
</head>

<body>

    <div class="a"></div>

    哈哈


    <script src="../js/flexble.js"></script>

</body>

</html>